Which raises another question.
If you are standing in a strong wind, do local obstructions significantly
effect measureed air pressure.? I would think that there could be a
significant difference between the air pressure on the upwind side of a
wall to the downwind side for example. - Or even standing in a strong wind
may reduce the pressure slightly  due to the moving air = less pressure
effect.

RP




Mike,

On Thu, 16 Sep 2004 09:38:22 -0500, Mike Hord wrote:

> I'm looking for a good, no-nonsense explanation of the variation of
> pressure with altitude.

To sum up, as long as you stay below about 20,000ft, pressure reduces by
1hPa (formerly millibar) per 10 metre
rise in altitude.  Sorry about the mixture of units, but this is what I can
remember!

Don't forget that atmospheric pressure varies with the weather, and I've
seen it fall really fast when a
serious Low comes in - I seem to remember 1hPa in 40 minutes, so don't
discount this if there's a really
strong wind!

> Basically what I want to know is this:  can I use a pressure
> sensor with an absolute range of up to 30 PSI to measure within
> 10 to 20 feet the difference in altitude between the current position
> of a sensor package and the position at which the package was
> initialized?  At altitudes of 1000 feet or less?

Yes, but the pressure change isn't very large - about 0.004psi over ten
feet.

Cheers,


Howard Winter
St.Albans, England


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